1. Field of the Invention
The invention relates to the deposition of a metal nitride-based layer on a transparent, and in particular, glass substrate with a view to producing glazings having protective properties with respect to solar radiation.
2. Discussion of the Background
Because the presence of nitride, such as titanium nitride layers on a glazing, such glazings make it possible to reduce in a room or cockpit the heat supply resulting from solar radiation by absorbing and reflecting the radiation.
Different methods exist for depositing metal nitride layers vacuum deposition include cathodic sputtering which is assisted by a magnetic field. This technique gives good results and makes it possible to obtain nitride layers having a perfectly controllable composition and a satisfactory colorimetry, with in particular, a grey color in transmission. Vacuum deposition can only be used discontinuously and requires complex equipment leading to a high production cost.
Pyrolytic methods and in particular, chemical vapor deposition (CVD) methods can also be used. These methods consist of contacting a substrate, which is raised to a high temperature, with metal and nitrogen precursors which, when heated, decompose to nitrides when contacted with the substrate.
These methods have the advantage of being usable in a continuous manner directly on a float glass ribbon, particularly in a float bath enclosure where the glass is already at an adequate pyrolytic temperature, without having to use constraining operating conditions, e.g. with regards to the pressure.
Thus, EP-B-128 169 describes the preparation of titanium nitride layers by vapor phase pyrolysis from a titanium precursor in the form of titanium tetrachloride and a nitrogen precursor in the form of ammonia. However, the described process imposes a strict control of the temperature conditions under which deposition takes place, so as to avoid, when the two precursors come into contact, the formation of a secondary reaction product in pulverulent form giving rise to a dirtying of the distribution device and possibly a reduction in the quality of the nitride film obtained by the formation of pits or milkiness on its surface.
It has also been found that the use of these two precursors without using strictly monitored operating conditions, particularly with regards to traces of impurities, moisture or oxidizing compounds of the oxygen type in the distribution equipment or when the temperature is not high enough lead to nitride layers which give the substrate (glass substrate type) which they cover a yellow-brown coloring in transmission and not the grey coloring which is e.g. obtained when using cathodic sputtering deposition methods. This color change results from the fact that the nitride layer differs slightly from the structural standpoint, chemically and/or electronically, more particularly, because of a certain content of impurities or elements other than the nitrogen or metal in question. However, this yellow or brown color is not particularly popular with building architects, because it gives a significant discoloration to the color of the sky which can be seen by a person within a room equipped with such a substrate as a glazing.
It is also known from U.S. Pat. No. 5,194,642 to use, for the deposition of a titanium nitride layer on a glass substrate, a single metal organic precursor containing both the necessary titanium and nitrogen atoms. This product, which is in pulverulent form, is the result of a reaction between a titanium halide and an amine, which takes place in two stages, the first at a relatively low temperature and under atmospheric pressure and the second under a partial vacuum at a much higher temperature. It is probable that the yield of such a reaction is not very high and it is also necessary to employ an additional stage of sublimating the precursor before spraying it onto the glass substrate. Thus, from the overall standpoint, the use of such a precursor tends to reduce the efficiency of the pyrolysis compared with the two starting constituents, makes the deposition process more complicated, and increases costs. A need therefore continues to exist for an improved method of providing a transparent substrate with a nitride layer of acceptable color.